Random Missfire 01gt

[Augustine72]

I have a 2001 GT with a random missfire. So far the scanner has picked up missfires in 2345cyls. It only happens under a load, it will not happen in park, neutral, or power brake.
I have replaced plugs and wires, swapped out coil packs and ignition modules. And it still happens. Primarily while accelerating from a rolling start and then when passing at highway speeds.

I am going to check that a signal is being sent to the injectors and test the injectors themselves.

Also if there is a way I would like to check the CPK, but it is a pain to pull.

I have checked the MAF but do not know the procedure for checking the EGR.

Any suggestions would be greatly appreciated.

[maxbfresh]

i have a similar problem with a 03 gt mine misfire around 4700 rpm at full throttle and around 5000 it stops, petal at full throttle wont accelerate never give me light at lower rmps tho. mine was in C1 i swapped injectors and now its random misfire. gm said it was PROBABLY the intake gaskets. just to be sure its po300 your getting right

[tblake]

How many miles are on your car? Have checked out the cat converter?

[richtazz]

Read this before proceeding any further (as Tim was referring to), as it is most likely your issue.

http://www.automotiveforums.com/vbul...d.php?t=681283

[Augustine72]

Ok so here is what is going on with this car plus a little background. 2001 GT
Car has 89k had 71k when we bought it about 2 years ago.
Up to last november I had replaced fuel filter, PS pump, alternator, and front brakes. Nothing too major. Then on our way home from Thanksgiving the transmission goes out. This is too early for problems with this tranny. I work at a tranny shop so we put an overhauled transmission in.

The car ran fine up until about 2 weeks ago when my wife(her car) began complaining about a shudder during acceleration. I took the car to work and hooked up the scanner.

No codes. I drove and watched the miss fire counter. The scanner recorded random miss fires in several cyls. So I replace plugs and wires, then drove. The shudder was still present.

Next I swapped coil packs and ignition modules with a known working set. The shudder continued.

Next I drove again using scan tool and recorded only one miss fire out of 3miles of driving. Shudder was still present.

Next, assuming the problem is still a miss fire and that the scanner is not picking it up, I checked the injectors as well as tested that a signal was being sent to the injectors from the computer. All was good.

Next I un hooked the EGR and drove, still a shudder.
Next I un hooked the MAF and drove, still a shudder.

I hooked up scan tool again and drove, the only codes were from when I drove the car with the EGR and MAF unplugged. Shudder is still present with no recorded miss fires.

I concluded that the miss fires were a seperate and unrelated issue to the shudder.

Today I drove and watched the TCC slip, thinking that it may be a transmission problem. And the converter showed excessive slip. However, I can not determine the cause.

If the TCC was bad it should set a code and shudder consistantly during when coming in and out of lock up.

It could either be a bad converter or low voltage being sent to the TCC causing it to slip in and out. It is possible that this is happening so fast that the computer fixes the problem before it can set a code.

So anybody want to buy a car?

[richtazz]

Welcome to AF BTW (forgot that in my first post)

The first thing I would do is check either exhaust backpressure at the front oxygen sensor hole or engine vacuum to eliminate a clogged converter as your issue. As RPM increases, an exhaust restriction will not allow the gases to escape, causing to much backpressure. This will result in misfires, poor mileage, no TCC lockup, etc...; basically every symptom you have and other than the misfires that occur as it really shudders, there will be no DTC set.

[Augustine72]

It has a new cat on it, with less than 2k. I can't imagine that it would have clogged up that quickly.

[tblake]

unless your car is running rich, overheated the cat and plugged it up.

[richtazz]

Was this stuttering issue the reason the converter was replaced?

You may be experiencing a condition commonly known as fishbite or chuggle. Do a forum search using those terms and see if the descriptions match what you're experiencing.

[Augustine72]

The transmission and converter were replaced at the same time. The converter went out on the original tranny sending metal through the pump and destroying 1st and 2nd gears.

We are going to do some more scanning to try and isolate what is causing the converter slippage.

Thanks I will let you all know what the cause was once we isolate it.